Outline

Hyaluronic acid (HA) is a component of the extracellular matrix (ECM) of human atherosclerotic plaques. HA is critically involved in the fine tuning of vascular smooth muscle cell (VSMC) proliferation and migration during atherosclerosis. HA-synthase 2 (HAS2), the major HAS-isoform in VSMC is induced by a variety of factors that modulate VSMC phenotype. Bioactive lysophospholipids such as sphingosylphosphorylcholine (SPC), lysophosphatidylcholine (LPC) and sphingosine-1-phosphat (S1P) are present in high-density lipoproteins (HDL) and are responsible for part of its vasodilatory and anti-apoptotic effects. The aim of the present study was to investigate whether bioactive lysophospholipids regulate HAS2 mRNA levels in human VSMC derived from human coronary arteries. VSMC were used between passages 4-10 and were cultured under normal growth conditions. After serum deprivation for 48 h, the cells were stimulated with the respective bioactive phospholipids for 6 hours. Compared with controls, HAS2 mRNA levels were induced by SPC (5 ÂµM) 1.8 Â± 0.3 fold and by LPC (15 ÂµM) 2.1 Â± 0.6 fold. In addition, HA levels were induced by SPC (5ÂµM) and LPC (15 ÂµM) as detected by immunohistochemistry using HA-binding protein. S1P (1 ÂµM) stimulated HAS2 expression 2.5 Â± 0.3 fold compared to control. S1P-and SPC-induced stimulation could be reversed with Tyrphostin SU1498 (30 ÂµM), a selective inhibitor of VEGF receptor kinase, and the effect of S1P was also abolished by Tyrphostin AG1296 (10 ÂµM), a specific PDGF receptor kinase inhibitor. Activation of the PDGF- and VEGF-receptors by their ligands PDGF-BB (10 ng/ml) and VEGF (45 ng/ml), respectively, induced HAS2 mRNA.

In conclusion, these findings demonstrate that bioactive lysophospholipids such as S1P activate HAS2 expression and HA-synthesis in VSMC, and that this may be mediated via a transactivation of the PDGF- and VEGF-receptors